1. Field of the Invention
The present invention relates to an electronic device, e.g., a foldable cellular phone set, having a bendable portion and, more particularly, to an electronic device in which the electrical connection of the bendable connecting portion is improved.
2. Description of the Prior Art
As shown in FIG. 1, a foldable cellular phone set 60 is comprised of one side portion 62 having a display screen 61 and the like, and the other side portion 72 having input buttons 63 and the like. The two side portions 62 and 72 are bendably connected at substantially their central position by a connecting portion 80, so they can be opened/closed. As shown in FIG. 2, one side portion 62 of the foldable cellular phone set 60 is comprised of a first front casing 64 and first back lid 66 that can be divided in the front and back directions. The other side portion 72 is similarly formed of a second front casing 74 and second back lid 76. The connecting portion 80 has a connecting member 80a on the first front casing 64 side and a connecting member 80b on the second front casing 74 side. The connecting members 80a and 80b are built in the connecting portion 80 together with other connecting members, so the connecting portion 80 is pivotal.
As shown in FIG. 3, one side portion 62 of the foldable cellular phone set has a first board 52, to which a liquid crystal panel for the display screen 61 and a receiver for producing the voice of the other party are to be connected, such that the board 52 is stored between the first front casing 64 and first back lid 66. The other side portion 72 has a second board 54, to which contact components of the input buttons 63 for inputting telephone numbers and the like and a microphone are to be connected, such that the board 54 is stored between the second front casing 74 and second back lid 76.
As shown in FIG. 3, the first and second boards 52 and 54 are electrically connected through a flexible FPC (Flexible Printed Circuit board) 50. The FPC 50 is connected at its one end to the first board 52 through a connector 56, and at its other end to the second board 54 through a connector 58. The FPC 50 is twisted by one turn to form one helical loop at its substantial center in the longitudinal direction, and is connected to the first and second boards 52 and 54. The first and second boards 52 and 54 are fixed to the first and second front casings 64 and 74, respectively, and the first and second back lids 66 and 76 are attached to the first and second front casings 64 and 74, respectively so the first and second boards 52 and 54 are stored. In this manner, since the FPC 50 is stored in the connecting portion 80 as it is twisted by one turn, one and the other side portions 62 and 74 respectively storing the first and second boards 52 and 54 can folded while maintaining electrical connection to each other.
In another prior art disclosed in Japanese Unexamined Patent Publication No. 11-308173, photocouplers are formed on those portions of two casings through which the casings are foldably connected to each other. The casings are electrically connected to each other through the photocouplers.
In the conventional foldable cellular phone set, the FPC connectors 56 and 58 are mounted on the respective boards. The two ends of the FPC 50 are fitted in the connectors 56 and 58, so the first and second boards 52 and 54 are electrically connected to each other. Hence, the manufacturing line requires the operation of building the FPC 50 to the connectors 56 and 58 and the like, which is cumbersome. Since the ends of the FPC 50 are thin, when they are to be fitted in the connectors, the connector 56 may be damaged, or the FPC 50 may undesirably bend. Furthermore, if the FPC 50 and connector 56 and the like are not sufficiently fitted with each other, they cause defective electrical connection, resulting in a defective product.
The FPC 50 is twisted into a loop in the connecting portion 80, and is usually in substantially tight contact with the inner surface of the connecting portion 80. When water enters through the connecting portion 80, capillarity occurs between the FPC 50 and the inner surface of the connecting portion 80, and the water may flow deeply into the connecting portion 80 to wet the first board 52 and the like. This causes corrosion of the first board 52 and the like to lead to a trouble or the like. As the FPC 50 runs from the inside to the outside of the connecting portion 80, the connecting portion 80 cannot be sealed completely.
As the functions of the cellular phone set increase, the amount of information transmitted between the first and second boards 52 and 54 increases. To transmit the information, it is required to increase the number of signal lines in the FPC 50. The space in the connecting portion 80 through which the FPC 50 can run is limited. If the width of the FPC 50 is increased in an attempt to increase the number of signal lines, the FPC 50 cannot run through the connecting portion 80. In addition, in recent years, demands for downsizing of the cellular phone set increase. To increase the width of the connecting portion 80 for the FPC 50 leads to an increase in size of the phone set main body, failing to downsizing. Information transmission using the FPC 50 is reaching its limit.
According to the invention disclosed in Japanese Unexamined Patent Publication No. 11-308173, the casings are electrically connected to each other through the photocouplers respectively provided to the two casings. The two photocouplers abut against each other when the respective casings are opened completely. During opening/closing operation, communication between the two photocouplers is disconnected.